Valve Assembly

ABSTRACT

There is provided a valve assembly including: a valve attached to a cylinder head in a movable manner along its axial line direction so as to selectively fluidly connect or close between a combustion chamber and a gas line; a plate-like holding member provided at the valve in a relatively immovable manner along the axial line direction; and a coil spring externally inserted around the valve in a state where its proximal end is directly or indirectly engaged to an external surface of the cylinder head, the coil spring being configured so that its distal end has a diameter smaller than that of the proximal end, wherein the holding member has an engaging surface facing one side along the axial line direction to hold the distal end of the coil spring.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a valve assembly applied to an internal combustion such as an automobile engine, two-wheeled vehicle engine and utility engine.

2. Related Art

The valve assembly is attached to a cylinder head of the internal combustion so as to selectively fluidly connect or block between a combustion chamber and a gas line.

The valve assembly includes a valve attached to the cylinder head in a movable manner to one side and the other side along its axial line direction and a coil spring for biasing the valve toward a blocking direction that is the other side along the axial line direction, where the combustion chamber and the gas line are fluidly connected when the valve is pushed to the one side along the axial line direction against a biasing force of the coil spring by way of a cam member.

The coil spring is externally inserted around the valve with its proximal end held at the cylinder head and its distal end held at a shaft portion of the valve.

A conventional valve assembly is configured such that the distal end of the coil spring is held at the shaft portion of the valve by a cotter, which is in form of halved shape and is externally inserted around the shaft portion of the valve, and a retainer, which is externally inserted around the cotter. In the thus configured conventional valve assembly, the structure for holding the distal end of the coil spring becomes larger and complicated. In consequence, the valve assembly as a whole becomes larger and heavier (see e.g., Japanese utility model unexamined publication No. H3-123914 and Japanese patent unexamined publication No. S57-10720).

Specifically, the shaft portion of the valve is formed with a concave portion on a distal end side.

The cotter in the form of halved shape has an inner peripheral surface formed with a convex portion that corresponds to the concave portion, and an outer peripheral surface tapered so as to have a diameter becoming larger as extending towards the other side along the axial line direction of the valve.

The retainer includes a main body portion having an inner peripheral surface tapered so as to correspond to the shape of the outer peripheral surface of the cotter, and a flange portion extending radially outward from an outer peripheral surface of the main body portion.

As described above, in the conventional valve assembly, the retainer for holding the distal end of the coil spring is immovable along the axial direction with respect to the valve by having the outer peripheral surface of the cotter tapered so as to have a diameter becoming larger as extending towards the other side in the axial direction (a direction away from the cylinder head), and by having the inner peripheral surface of the retainer tapered so as to contact the tapered outer peripheral surface of the cotter. Consequently, the cotter and the retainer become larger and complicated, resulting in enlarging and weighting the valve assembly.

In Japanese patent unexamined publication No. 2004-60616, there is proposed a valve assembly having another configuration in which a holding member having a circular shape in cross section is provided in place of the cotter.

Such a conventional valve assembly is believed to achieve reduction in cost and weight according to the configuration.

However, in the configuration described in Japanese patent unexamined publication No. 2004-60616, the inner peripheral surface of the retainer is tapered so as to have a diameter becoming larger as extending toward the other side along the axial direction (a direction away from the cylinder head), and the retainer is configured so as to have a flange portion extending radially outward from a largest diameter portion of the tapered inner peripheral surface, the flange portion holding the coil spring.

In such a configuration, the distal end of the coil spring cannot be sufficiently brought close to the shaft portion of the valve, and consequently, a large bending moment is applied on the retainer and the holding member. Therefore, the retainer and the holding member are required to have strength enough to withstand the bending moment, which leads to increase in size and weight.

SUMMARY OF THE INVENTION

In consideration of the above prior art, it is an object of the present invention to provide a valve assembly that is applied to an internal combustion, the valve assembly being capable of holding a distal end of a coil spring at a position close to a shaft portion of a valve as much as possible, thereby achieving reduction in size and weight while having a simple configuration.

A first aspect of the present invention provides, in order to achieve the object, a valve assembly including: a valve attached to a cylinder head in a movable manner along its axial line direction so as to selectively fluidly connect or close between a combustion chamber and a gas line; a plate-like holding member provided at the valve in a relatively immovable manner along the axial line direction; and a coil spring externally inserted around the valve in a state where its proximal end is directly or indirectly engaged to an external surface of the cylinder head, the coil spring being configured so that its distal end has a diameter smaller than that of the proximal end, wherein the holding member has an engaging surface facing one side along the axial line direction to hold the distal end of the coil spring.

According to the first aspect of the present invention, it is possible to hold the distal end of the coil spring at the position close to the shaft portion of the valve as much as possible. Consequently, a bending moment applied from the coil spring to the holding member could be reduced, thereby achieving reduction in weight and size of the entire valve assembly.

Preferably, the coil spring may have a concave portion, into which the holding member is engaged, at an end surface of the distal end.

Preferably, the holding member may include a center hole having a diameter larger than an outer diameter of a concave groove formed at a shaft portion of the valve and smaller than an outer diameter of the shaft portion, and a slit opening the center hole to outside.

Further, a second aspect of the present invention provides, in order to achieve the object, a valve assembly including: a valve attached to a cylinder head in a movable manner along its axial line direction so as to selectively fluidly connect or close between a combustion chamber and a gas line; a plate-like holding member provided at the valve in a relatively immovable manner along the axial line direction, the holding member having an engaging surface facing one side along the axial line direction; a plate-like retainer externally inserted around the valve in a relatively movable manner along the axial line direction in a state where its inner peripheral surface slidably contacts an outer peripheral surface of the valve, the retainer having a contacting surface that faces the other side along the axial line direction and contacts the engaging surface of the holding member so that an end of a movable area of the retainer towards the other side along the axial line direction is defined; and a coil spring externally inserted around the valve in a state where its proximal end is directly or indirectly engaged to an external surface of the cylinder head, the coil spring being configured so that its distal end has a diameter smaller than that of the proximal end, wherein the retainer has a supporting surface facing the one side along the axial line direction to hold the distal end of the coil spring.

According to the second aspect of the present invention, it is possible to hold the distal end of the coil spring at the position close to the shaft portion of the valve as much as possible. Consequently, a bending moment applied from the coil spring to the retainer and the holding member could be reduced, thereby achieving reduction in weight and size of the entire valve assembly.

In the second aspect of the present invention, the retainer may preferably have an outer diameter smaller than an inner diameter of the proximal end of the coil spring.

In the above various configurations according to the first and second aspects of the present invention, the valve may be inserted into an axial line hole of a valve guide in a movable manner along the axial line direction, the valve guide being fixed to the cylinder head.

In the configuration, the coil spring may preferably have an enlarged diameter portion extending from the proximal end towards the other side along the axial line direction so as to surround the valve guide, and a tapered portion that has a diameter becoming smaller as extending from the enlarged diameter portion towards the other side along the axial line direction and terminates at the distal end.

Preferably, the inner diameter of the distal end of the coil spring may be smaller than the outer diameter of the valve guide.

In the above various configurations according to the first and second aspects of the present invention, the valve preferably includes a stem member and a lid member. The stem member includes a shaft portion and a flare portion extending towards the one side along the axial line direction from the shaft portion. The stem member has a hollow portion of which the flare portion is an open end. The lid member is fixed to the flare portion of the stem member by caulking.

The flare portion includes an enlarged diameter portion and a reduced diameter portion. The enlarged diameter portion has a diameter becoming larger as extending towards the one side along the axial line direction. The reduced diameter portion extends from the enlarged diameter portion towards the one side along the axial line direction with a flexion point in between, and intersects the enlarged diameter portion in a longitudinal cross sectional view.

The lid member is sandwiched by the enlarged diameter portion and the reduced diameter portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, and other objects, features and advantages of the present invention will become apparent from the detailed description thereof in conjunction with the accompanying drawings wherein.

FIG. 1 is a partial schematic cross sectional view showing one example of an internal combustion to which a valve assembly according to a first embodiment of the present invention is applied.

FIG. 2 is a longitudinal cross sectional view of a valve of the valve assembly according to the first embodiment.

FIG. 3 is a longitudinal cross sectional view of another valve, which is modified from the valve shown in FIG. 2.

FIG. 4 is a longitudinal cross sectional view of still another valve, which is modified from the valve shown in FIG. 2.

FIG. 5 is a longitudinal cross sectional view of still another valve, which is modified from the valve shown in FIG. 2.

FIG. 6 is a plan view of a holding member of the valve assembly according to the first embodiment, FIGS. 6( a)-(c) show examples of the holding member.

FIG. 7 is a partial longitudinal cross sectional view in the vicinity of the holding member and a retainer of the valve assembly according to the first embodiment, FIGS. 7( a)-(d) show examples of the retainer.

FIG. 8 is a partial cross sectional view of a valve assembly according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

A preferred embodiment of a valve assembly according to the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a partial schematic cross sectional view showing one example of an internal combustion 500 (engine) to which a valve assembly 100 according to the present embodiment is applied.

The internal combustion 500 shown in FIG. 1 includes a cylinder head 600 formed with a combustion chamber 610, a fuel gas supply line 620 for supplying fuel gas to the combustion chamber 610, a fuel gas discharge line 630 for discharging the gas that has been combusted in the combustion chamber 610, and valve assemblies 100 according to the present embodiment respectively provided in the fuel gas supply line 620 and the fuel gas discharge line 630 to perform an open-close control of the lines 620, 630.

The valve assembly 100 is attached to the cylinder head 600 so as to open or close ports 620P, 630P of the corresponding gas lines 620, 630 with respect to the combustion chamber 610, the ports 620P, 630P being configured to fluidly connect the corresponding gas lines 620, 630 to the combustion chamber 610.

Specifically, as shown in FIG. 1, the valve assembly 100 includes: a valve 1 attached to the cylinder head 600 in a movable manner along the axial line direction; a holding member 40 fixed to the valve 1 in a relatively immovable manner along the axial line direction; a plate-like retainer 50 externally inserted around the valve 1 in a relatively movable manner along the axial line direction in a state where its inner peripheral surface 51 slidably contacts an outer peripheral surface of the valve 1, the retainer 50 being configured so that an end of a movable area thereof towards the other side along the axial line direction (a direction away from the cylinder head 600) is defined by the holding member 40; and a coil spring 60 having a proximal end held at an external surface of the cylinder head 600 and a distal end held at the retainer 50, the coil spring 60 biasing the valve 1 towards the other side along the axial line direction by way of the retainer 50 and the holding member 40.

The valve assembly 100 is configured so as to selectively fluidly connect or close the corresponding ports 620P, 630P by a driving mechanism provided in the internal combustion 500.

That is, the driving mechanism includes a cam member 720 rotatably driven about the axial line by a driving shaft 710.

The valve 1 is configured to take an opening position where the corresponding port 620P, 630P is fluidly connected to the combustion chamber 610 when the cam member 72 operatively pushes the valve 1 towards one side along the axial line direction (a direction close to the cylinder head 600) against a biasing force of the coil spring 60, and a blocking position where the corresponding port 620P, 630P is closed with respect to the combustion chamber 610 by the biasing force of the coil spring 60 when the pushing force by the cam member 72 is not applied.

FIG. 1 shows a state in which both of the fuel gas supply line 620 and the fuel gas discharge line 630 are blocked with respect to the combustion chamber 610 by the corresponding valve assembly 100.

FIG. 2 shows a longitudinal cross sectional view of the valve 1.

As shown in FIGS. 1 and 2, the valve 1 has a shaft portion 11 and a flare portion 12 extending towards the one side along the axial line direction from the shaft portion 11.

The shaft portion 11 is supported at the cylinder head 600 in a movable manner along the axial line direction.

Specifically, the cylinder head 600 is fixedly provided with a hollow valve guide 650 having an axial line hole (see FIG. 1), and the shaft portion 11 is inserted into the axial line hole of the valve guide 650 in a slidable manner along the axial line direction.

Reference number 660 in FIG. 1 designates a seal member for sealing a space between an upper opening end of the axial line hole in the valve guide 650 and the shaft portion 11.

The flare portion 12 is configured so as to sit on a valve seat of the corresponding port 620P, 630P to close the corresponding port 620P, 630P with respect to the combustion chamber 610 when the valve 1 is positioned at the blocking position, and move away from the valve seat to fluidly connect the corresponding port 620P, 630P with respect to the combustion chamber 610 when the valve 1 is positioned at the opening position.

In the present embodiment, the valve 1 includes a stem member 10 in which the shaft portion 11 and the flare portion 12 are integrally formed.

The stem member 10 has a hollow shape having a hollow portion 15 of which the flare portion 12 is an open end.

The stem member 10 is formed by drawing a plate shaped member of steel, heat resisting steel, stainless, titanium alloy and the like.

The valve 1 further has a lid member 20 coupled to the open end of the flare portion by caulking so as to close the hollow portion 15 of the stem member 10.

The lid member 20 is formed of the plate shaped member of steel, heat resisting steel, stainless, titanium alloy and the like.

With the configuration where the valve 1 has a hollow shape as described above, it is possible to reduce the weight of the valve assembly 100 as a whole.

Specifically, the lid member 20 has a center portion that has an upper surface facing the hollow portion, and a peripheral portion that extends radially outward from the center portion with the axial line X of the shaft portion 10 as a reference, the peripheral portion being coupled to the stem member 10.

In the embodiment shown in FIG. 2, the center portion has a flat plate shape that is substantially orthogonal to the axial line X, but the center portion may have a convex shape or a concave shape when seen in a longitudinal cross sectional view.

Reference number 19 in FIG. 2 designates a plug inserted into the shaft portion 10 to close an end on the opposite side of the open end of the hollow portion 15. The plug 19 is caulked while being inserted into the hollow portion 15 of the shaft portion 10.

The valve 1 preferably includes a powder coolant 30 in an internal space 15 defined by the stem member 10 and the lid member 20, as shown in FIG. 2.

In a case where the powder coolant 30 is provided as described above, the valve 1 is formed by coupling the lid member 20 to the stem member 10 by caulking in a state where the powder coolant 30 has been accommodated in advance in the hollow portion 15 of the stem member 10.

A powder body of aluminum nitride or ceramics having an average particle diameter of 1 μm or more may be used as the powder coolant 30.

In the present embodiment, the valve 1 also has the following configuration.

As shown in FIG. 2, in a state after the peripheral portion of the lid member 20 is coupled to the stem member 10 by caulking, the flare portion 12 of the stem member 10 has an enlarged diameter portion 12 a having a diameter becoming larger as extending towards the one side (i.e., the open end side of the hollow portion 15) with the axial line X of the shaft portion 11 as the reference, and a reduced diameter portion 12 c extending from the enlarged diameter portion 12 a towards the one side with a flexion point 12 b in between.

Specifically, the reduced diameter portion 12 c is configured to intersect the enlarged diameter portion 12 a in a longitudinal cross sectional view.

That is, the enlarged diameter portion 12 a and the reduced diameter portion 12 c are configured such that an outline in the longitudinal cross sectional view of the enlarged diameter portion 12 a and an outline in the longitudinal cross sectional view of the reduced diameter portion 12 c intersect at a predetermined angle rather than being substantially parallel. The lid member 20 is sandwiched by the enlarged diameter portion 12 a and the reduced diameter portion 12 c, as shown in FIG. 2.

The valve 1 with the configuration could effectively prevent the pressure of the hollow portion from being raised 15 during operation of the internal combustion, while reducing the weight by making the stem member 10 into the hollow shape and effectively suppressing the rise of the temperature thanks to the powder coolant 30 accommodated in the hollow portion 15 of the stem member 10.

Specifically, since the valve 1 is arranged so as to face the combustion chamber 610, the valve 1 is normally exposed to high temperature of about 450° C. when provided in the fuel gas supply line 620 and of about 800° C. when provided in the fuel gas discharge line 630 during the operation of the internal combustion.

Therefore, the stem member 10 may tend to expand and deform due to the rise of the internal pressure of the hollow portion 15 even if the temperature rise of the stem member 10 is alleviated to some extent by the coolant 30 accommodated in the hollow portion 15 of the stem member 10.

In particular, in a case where the thickness of the stem member 10 is made thin in order to reduce the weight of the stem member 10, such risk becomes higher.

In this regards, the valve 1 is configured such that the lid member 20 is coupled to the flare portion 12 of the stem member 10 by caulking so as to be sandwiched by the enlarged diameter portion 12 a and the reduced diameter portion 12 c, and the reduced diameter portion 12 c intersects the enlarged diameter portion 12 a in the longitudinal cross sectional view after caulking.

With such a configuration, when the valve 1 is exposed to high temperature during the operation of the internal combustion, the flexion point 12 b between the enlarged diameter portion 12 a and the reduced diameter portion 12 c thermally expands radially outward with the axial line X of the shaft portion 11 as the reference, whereby a gap, which fluidly connects the hollow portion 15 to outside while preventing the accommodated powder coolant 30 from leaking outside, is created between the stem member 10 and the lid member 20.

Therefore, the rise of the internal pressure of the hollow portion 15 due to the temperature rise is effectively prevented, thereby preventing the deformation of the stem member 10.

Furthermore, in the present embodiment, the valve 1 is configured so as to relieve the internal pressure of the hollow portion 15 to outside through the gap that opens to the combustion chamber 610. Therefore, it is possible to suppress the rise of the internal pressure rise of the hollow portion 15 while effectively preventing the engine oil from being mixed into the valve 1 and preventing the valve 1 from being damaged.

Specifically, if an internal pressure escape hole is provided in the vicinity (portion A of FIG. 2) at the other end (an end on the opposite side of the flare portion 12) of the shaft portion 11, the engine oil may flow into the hollow portion 15 of the valve 1.

If the internal pressure escape hole is provided at the portion (portion B of FIG. 2) lying from the shaft portion 11 to the flare portion 12, the vicinity of the internal pressure escape hole becomes a stress concentration area, whereby the stem member 10 may be broken.

On the other hand, the valve 1 is configured so that the gap created between the stem member 10 and the lid member 20 is used as the internal pressure escape hole. That is, in the valve 1, the internal pressure escape hole is positioned in the combustion chamber 610. Therefore, it is possible to suppress the rise of the internal pressure of the hollow portion 15 while effectively preventing the engine oil from being mixed into the valve 1 and preventing the valve 1 from being damaged.

In a configuration where the lid member 20 is arranged so as to be substantially orthogonal to the shaft portion 11 of the stem member 10 as shown in FIGS. 1 and 2, the reduced diameter portion 12 c is preferably formed so as to approach the axial line X of the shaft portion 11 as extending towards the one side (i.e. a free end side).

According to such a configuration, the flexion point 12 b easily expands radially outward with the axial line X of the shaft portion 11 as the reference during thermal expansion of the stem member 10, whereby the gap is more reliably obtained.

Preferably, the stem member 10 may be formed of a material having a thermal expansion coefficient larger than that of the lid member 20.

For example, the stem member 10 may be formed of SUS305 (linear thermal expansion coefficient 16×10⁻⁶° C. in a temperature range of 0° C. to 100° C.), and the lid member 20 may be formed by SUH3 (linear thermal expansion coefficient 11×10⁻⁶° C. in a temperature range of 0° C. to 100° C.).

By forming the stem member 10 with a material that tends to thermally expand more easily than the lid member 20 as described above, the gap could be reliably formed between the stem member 10 and the lid member 20 in the operation of the internal combustion.

In FIGS. 1 and 2, the lid member 20 has a simple flat plate shape, but a lid member 20′ having a concave portion 21 a that opens towards inside the hollow portion 15 of the stem member 10 may be provided in place thereof (see FIGS. 3 to 5).

By providing the lid member 20′ having the concave portion at an upper surface facing the hollow portion 15 of the center portion as shown in FIG. 3, the powder coolant 30 could be effectively prevented from leaking out to outside even if the amount of thermal expansion of the stem member 10 becomes too large so that the gap becomes greater than the particle diameter of the powder coolant 30.

Since the modified embodiment shown in FIG. 3 is configured so that the concave portion is formed by bending a peripheral edge of the lid member 20′ upward, a contacting area between the lid member 20′ and the stem member 10 could be increased. With the configuration, it is possible to effectively transmit the heat, which the lid member 20′ has received, to the enlarged diameter portion 12 a and the flexion point 12 b, thereby enhancing the durability of the lid member 20′ and thinning the lid member 20′ while effectively preventing the leakage of the powder coolant 30.

In the embodiment shown in FIG. 3, the thickness of a region, which contacts the enlarged diameter portion 12 a, out of the lid member 20′ may be preferably made thinner than the thickness of the other regions so that the lid member 20′ can be attached to the stem member 10 in an elastically deformed state.

With the configuration, the gap between the stem member 10 and the lid member 20′ could be made smaller.

Moreover, a thick lid member 20′ may be used, which has a depression at the upper surface facing the hollow portion 15 in the center portion, and the depression could be used as the concave portion, as shown in FIG. 4 and FIG. 5. With the thick lid member 20′, the caulking amount of the stem member 11 could be increased (see FIG. 4). Therefore, it is possible to increase the contacting area between the lid member 20′ and the stem member 11 so that the leakage of the powder coolant 30 is effectively prevented.

However the above described various valves are configured so that the lid member 20 is coupled to the flare portion 12 only by caulking, the lid member 20 could be coupled to the flare portion by welding a part of the peripheral edge of the lid member 20 to the flare portion 12 as long as the gap is created between the lid member 20 and the flare portion 12 thanks to the thermal expansion in the operation of the internal combustion.

The coil spring 60 is configured so that the outer diameter at the distal end that is held at the retainer 50 is smaller than the outer diameter at the proximal end that is held at the cylinder head 600, as shown in FIG. 1.

In the present embodiment, the coil spring 60 has an enlarged diameter portion 61 extending from the proximal end towards the other side along the axial line direction so as to surround the valve guide 650, and a tapered portion 65 that has a diameter becoming smaller as extending from the enlarged diameter portion 61 towards the other side along the axial line direction and terminates at the distal end.

The enlarged diameter portion 61 has an inner diameter larger than the outer diameter of the valve guide 650.

The tapered portion 65 is configured so that the inner diameter at the distal end is smaller than the outer diameter of the valve guide 650.

In the present embodiment, the plate-like retainer 50, which is configured so that the end of the movable area of the retainer 50 towards the other side along the axial line direction is defined by the plate-like holding member 40, holds the distal end of the coil spring 60, thereby bringing the distal end of the coil spring 60 close to the shaft portion 11 of the valve 10 as much as possible.

Specifically, the conventional valve assembly is configured so that the distal end of the coil spring is held by way of the cotter having a tapered outer peripheral surface and the retainer having a tapered inner peripheral surface, as described in the section of the Related Art.

In such a conventional configuration, the thickness (i.e. a radial width with the shaft portion of the valve as the reference) of the cotter and the retainer becomes thicker due to the necessity of forming the tapered surfaces. Consequently, the distal end of the coil spring cannot be brought close to the shaft portion of the valve, resulting in applying a large bending moment onto the cotter and the retainer for holding the distal end of the coil spring.

On the other hand, in the present embodiment, the distal end of the coil spring 60 is supported by the plate-like holding member 40 and the plate-like retainer 50.

Specifically, the shaft portion 11 is formed with a concave groove that opens radially outward at the external surface on the other side along the axial line direction.

The holding member 40 is a plate-like ring member that engages into the concave groove.

FIG. 6( a) is a plan view of the holding member 40.

As shown in FIG. 6( a), the holding member 40 has a center hole 41 and a slit 42 for opening the center hole 41 to outside.

Specifically, the center hole 41 has a diameter that is larger than the outer diameter of the concave groove and that is smaller than the outer diameter of the shaft portion 11.

The slit 42 forms a passage through which the shaft portion 11 is passed when attaching or detaching the holding member 40 to or from the shaft portion 11, and has a shape and an opening width that enables the holding member 40 to elastically deform when attaching or detaching the holding member 40 to or from the shaft portion 11.

In addition to the above configuration, the holding member 40 a may be provided with a cutout portion 43 opening to the center hole 41 (see FIG. 6( b)).

By providing the cutout portion 43 in the holding member 40, it is possible to further reduce the weight thereof and facilitate the elastic deformation thereof.

FIG. 7( a) shows a partial longitudinal cross sectional view in the vicinity of the holding member 40 and the retainer 50 of the valve assembly 100.

The retainer 50 is a ring member that is externally inserted around the shaft portion 11 in a relatively movable manner along the axial line direction in a state that its inner peripheral surface 51 in form of cylindrical shape contacts the outer peripheral surface of the shaft portion 11 and that is contacted to a first end surface facing the one side along the axial line direction of the holding member 40 so that the end of the movable area of the retainer 50 towards the other side along the axial line direction is defined.

That is, the holding member 40 is configured so that the first end surface facing the one side along the axial line direction forms an engaging surface 40 a contacting the retainer 50 (see FIG. 7( a)).

The retainer 50 is guided by contacting the inner peripheral surface 51 to the outer peripheral surface of the shaft portion 11 in a slidable manner, and is configured so that a first end surface facing the one side along the axial line direction forms a supporting surface 50 b that engages the distal end of the coil spring 60 and a second end surface facing the other side along the axial line direction forms a contacting surface 50 a that contacts the engaging surface 40 a of the holding member 40 (see FIG. 7( a)).

In the present embodiment, the retainer 50 has a concave portion at the second end surface as shown in FIGS. 1 and 7( a).

The concave portion has a shape and a size enabling the holding member 40 to be engaged into.

That is, in the present embodiment, a bottom surface of the concave portion forms the contacting surface 50 a and an inner peripheral surface of the concave portion prevents radially outward deformation of the holding member 40.

The retainer 50 may take various shapes as long as the first end surface facing the one side along the axial line direction forms the supporting surface 50 b and the second end surface facing the other side along the axial line direction forms the contacting surface 50 a in a state where the inner peripheral surface 51 of cylindrical shape is guided by the outer peripheral surface of the shaft portion 11.

The retainer 50 may be configured to include a ring portion having the supporting surface 50 b and the contacting surface 50 a, and an internal cylinder portion integrally extending to the one side along the axial line direction from the inner end in the radial direction of the ring portion, as shown in FIG. 7( a), or in place thereof or in addition thereto, may be configured to include the ring portion and an external cylinder portion integrally extending to the one side along the axial line direction from the outer end in the radial direction of the ring portion, as shown in FIG. 7( b).

The configuration including the internal cylinder portion as shown in FIG. 7( a) could elongate the length along the axial line direction of the inner peripheral surface 51, whereby orientation of the retainer 50 with respect to the shaft portion 11 can be stabilized.

The configuration including the external cylinder portion as shown in FIG. 7( b) could stably hold the distal end of the coil spring 60.

Further, it is obviously possible that the retainer 50 is formed only by the ring portion, as shown in FIG. 7( c). Furthermore, it is possible that the retainer 50 is formed only by the ring portion and the outer end in the radial direction on a side of the contacting surface 50 a of the ring portion is chamfered, as shown in FIG. 7( d).

In the embodiment where the concave portion, into which the holding member 40 is to be engaged (see FIGS. 7( a) to 7(d)), is formed at the surface facing the holding member 40 (the second end surface along the axial line direction) of the retainer 50 as described above, it is also possible that the holding member 40 is formed by a plurality of halved bodies 45, 45 as shown in FIG. 6( c).

The retainer 50 preferably has the outer diameter smaller than the inner diameter of the proximal end of the coil spring 60.

According to such a configuration, the bending moment acting on the retainer 50 from the coil sprint 60 is further reduced.

Preferably, it may be configured so that at least a part of the distal end of the coil spring 60 overlaps with the holding member 40 when seen along the axial line direction of the shaft portion 11, thereby supporting the distal end of the coil spring in a more stable manner.

Embodiment 2

Another embodiment of the valve assembly according to the present invention will now be described with reference to the accompanying drawings.

FIG. 8 shows a partial cross sectional view of a valve assembly 100B according to the present embodiment.

In the drawing, same reference characters are denoted for the same members as in embodiment 1, and the description thereof will not be repeated.

While the above described valve assembly 100 according to the Embodiment 1 is configured such that the distal end of the coil spring 60 is held by the plate-like retainer 50, the valve assembly 100B according to the present embodiment is configured such that the distal end of a coil spring 60B is held by the engaging surface 40 a of the holding member 40.

That is, the valve assembly 100B is configured so that the plate-like retainer 50 is omitted and a coil spring 60B in place of the coil spring 60 is provided with respect to the valve assembly 100 according to Embodiment 1.

The coil spring 60B differs from the coil spring 60 only in that a concave portion is formed in an end surface at the distal end.

The concave portion has a size and a shape enabling the holding member 40 to be engaged into.

The valve assembly 100B having the above configuration could also achieve reduction in size and weight, similarly to the Embodiment 1.

This specification is by no means intended to restrict the present invention to the preferred embodiments and the modified embodiments set forth therein. Various modifications to the valve assembly may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims. 

1. A valve assembly comprising: a valve attached to a cylinder head in a movable manner along its axial line direction so as to selectively fluidly connect or close between a combustion chamber and a gas line; a plate-like holding member provided at the valve in a relatively immovable manner along the axial line direction; and a coil spring externally inserted around the valve in a state where its proximal end is directly or indirectly engaged to an external surface of the cylinder head, the coil spring being configured so that its distal end has a diameter smaller than that of the proximal end, wherein the holding member has an engaging surface facing one side along the axial line direction to hold the distal end of the coil spring.
 2. A valve assembly according to claim 1, wherein the coil spring has a concave portion, into which the holding member is engaged, at an end surface of the distal end.
 3. A valve assembly according to claim 1, wherein the holding member includes a center hole having a diameter larger than an outer diameter of a concave groove formed at a shaft portion of the valve and smaller than an outer diameter of the shaft portion, and a slit opening the center hole to outside.
 4. A valve assembly comprising: a valve attached to a cylinder head in a movable manner along its axial line direction so as to selectively fluidly connect or close between a combustion chamber and a gas line; a plate-like holding member provided at the valve in a relatively immovable manner along the axial line direction, the holding member having an engaging surface facing one side along the axial line direction; a plate-like retainer externally inserted around the valve in a relatively movable manner along the axial line direction in a state where its inner peripheral surface slidably contacts an outer peripheral surface of the valve, the retainer having a contacting surface that faces the other side along the axial line direction and contacts the engaging surface of the holding member so that an end of a movable area of the retainer towards the other side along the axial line direction is defined; and a coil spring externally inserted around the valve in a state where its proximal end is directly or indirectly engaged to an external surface of the cylinder head, the coil spring being configured so that its distal end has a diameter smaller than that of the proximal end, wherein the retainer has a supporting surface facing the one side along the axial line direction to hold the distal end of the coil spring.
 5. A valve assembly according to claim 4, wherein the retainer has an outer diameter smaller than an inner diameter of the proximal end of the coil spring.
 6. A valve assembly according to claim 1, wherein the valve is inserted into an axial line hole of a valve guide in a movable manner along the axial line direction, the valve guide being fixed to the cylinder head; and the coil spring has an enlarged diameter portion extending from the proximal end towards the other side along the axial line direction so as to surround the valve guide, and a tapered portion that has a diameter becoming smaller as extending from the enlarged diameter portion towards the other side along the axial line direction and terminates at the distal end.
 7. A valve assembly according to claim 6, wherein the inner diameter of the distal end of the coil spring is smaller than the outer diameter of the valve guide.
 8. A valve assembly according to claim 1, wherein the valve comprises a stem member that includes a shaft portion and a flare portion extending towards the one side along the axial line direction from the shaft portion, the stem member having a hollow portion of which the flare portion is an open end, and a lid member fixed to the flare portion of the stem member by caulking; the flare portion includes an enlarged diameter portion having a diameter becoming larger as extending towards the one side along the axial line direction and a reduced diameter portion extending from the enlarged diameter portion towards the one side along the axial line direction with a flexion point in between, the reduced diameter portion intersecting the enlarged diameter portion in a longitudinal cross sectional view; and the lid member is sandwiched by the enlarged diameter portion and the reduced diameter portion. 